1. Field of the Invention
The present invention relates to a digital communication system, and more particularly, to a digital television (DTV) transmitter and a method of coding data in a DTV transmitter.
2. Discussion of the Related Art
8T-VSB transmission of digital broadcast transmissions has been developed to transmit MPEG video/audio data, and was adopted as digital broadcast standard in North America and the Republic of Korea. With rapid development of digital signal processing technology and spread of the Internet, more and more technologies for digital appliances, computers and internet technology are being integrated. Therefore, it is necessary to develop systems to transmit various supplemental data as well as video/audio data to users via digital broadcast channels to satisfy users' demands.
Some of digital data broadcast users will use the supplemental data broadcast through a PC card or a portable device to which an indoor antenna is installed. However, when such a PC card and the portable device are used indoors, broadcast receiving performance is significantly decreased as intensities of broadcast signals are seriously reduced by walls and moving objects indoors and ghost images and noise are generated by reflection waves. Especially, transmission of the supplemental data must have a relatively low error rate unlike that of general video/audio data. Namely, although the video/audio data has errors therein during its transmission, if the errors are errors which cannot be detected by users' ears and eyes, there may be no problems. On the other hand, when the supplemental data (for example, an application program execution file, stock information, etc.) has an error, the error, of even one bit, may cause a serious problem. Therefore, it is needed to develop a system which is resistant against ghost images and noise which may be generated in channels.
Transmission for supplemental data is generally performed through a channel identical to an MPEG video/audio channel, on the basis of time division method. On the other hand, after digital broadcasting has started, ATSC VSB digital broadcast receiver, which is capable of receiving only MPEG video/audio, has been widely sold on the market. Therefore, the supplemental data, which is transmitted through channel identical to an MPEG video/audio channel, must not affect the conventional ATSC VSB dedicated receivers that have been sold on the market, which can be defined as “ATSC VSB compatible.” Considering such conditions, newly developed supplemental data broadcast system must be compatible with the ATSC VSB system. Here, the supplemental data is also referred to as enhanced data or E-VSB data.
Also, the conventional ATSC VSB receiving system suffers from deteriorated receiving performance in bad channel environments. Especially, portable and mobile receivers require resistance against channel variation and noise.